Sensing of body fluid hormones using paper-based analytical devices

A Hypothetical Approach to Concentrate Microorganisms from Human Urine Samples Using Paper-Based Adsorbents for Point-of-Care Molecular Assays

This hypothesis demonstrates that the efficiency of loop-mediated isothermal amplification (LAMP) for nucleic acid detection can be positively influenced by the preconcentration of microbial cells onto hydrophobic paper surfaces. The mechanism of this model is based on the high affinity of microbes towards hydrophobic surfaces. Extensive studies have demonstrated that hydrophobic surfaces exhibit enhanced bacterial and fungal adhesion. By exploiting this inherent affinity of hydrophobic paper substrates, the preconcentration approach enables the adherence of a greater number of target cells, resulting in a higher concentration of target templates for amplification directly from urine samples. In contrast to conventional methods, which often involve complex procedures, this approach offers a simpler, cost-effective, and user-friendly alternative. Moreover, the integration of cell adhesion, LAMP amplification, and signal readout within paper origami-based devices can provide a portable, robust, and highly efficient platform for rapid nucleic acid detection. This innovative hypothesis holds significant potential for point-of-care (POC) diagnostics and field surveillance applications. Further research and development in this field will advance the implementation of this technology, contributing to improved healthcare systems and public health outcomes.

Hair and Nail-On-Chip for Bioinspired Microfluidic Device Fabrication and Biomarker Detection

The advent of biosensors has tremendously increased our potential of identifying and solving important problems in various domains, ranging from food safety and environmental analysis, to healthcare and medicine. However, one of the most prominent drawbacks of these technologies, especially in the biomedical field, is to employ conventional samples, such as blood, urine, tissue extracts and other body fluids for analysis, which suffer from the drawbacks of invasiveness, discomfort, and high costs encountered in transportation and storage, thereby hindering these products to be applied for point-of-care testing that has garnered substantial attention in recent years. Therefore, through this review, we emphasize for the first time, the applications of switching over to noninvasive sampling techniques involving hair and nails that not only circumvent most of the aforementioned limitations, but also serve as interesting alternatives in understanding the human physiology involving minimal costs, equipment and human interference when combined with rapidly advancing technologies, such as microfluidics and organ-on-a-chip to achieve miniaturization on an unprecedented scale. The coalescence between these two fields has not only led to the fabrication of novel microdevices involving hair and nails, but also function as robust biosensors for the detection of biomarkers, chemicals, metabolites and nucleic acids through noninvasive sampling. Finally, we have also elucidated a plethora of futuristic innovations that could be incorporated in such devices, such as expanding their applications in nail and hair-based drug delivery, their potential in serving as next-generation wearable sensors and integrating these devices with machine-learning for enhanced automation and decentralization.

Tuning Hydrophobicity of Paper Substrates for Effective Colorimetric detection of Glucose and Nucleic acids

This study investigated the colorimetric response of standard glucose, serum glucose, and nucleic acid assays on various paper surfaces with different wettability, including hydrophilic, hydrophobic, and nearly superhydrophobic surfaces. Water contact angles (WCA) formed by water droplets on each surface were measured using ImageJ software. The hydrophilic surface showed no contact angle, while the hydrophobic and nearly superhydrophobic surfaces exhibited contact angles of 115.667° and 133.933°, respectively. The colorimetric sensitivity of the standard glucose assay was analyzed on these surfaces, revealing enhanced sensitivity on the nearly superhydrophobic surface due to the high molecular crowding effect owing to its non-wetting behavior and eventually confined reaction product at the sample loading zone. The hydrophobic nature of the surface restricts the spreading and diffusion of the reaction product, leading to a controlled and localized concentration of the assay product leading to moderate colorimetric intensity. On the other hand, the hydrophilic surface showed the least enhancement in colorimetric sensitivity; this is attributed to the high wettability of the hydrophilic surface causing the reaction product to spread extensively, resulting in a larger area of dispersion and consequently a lower colorimetric intensity. The measured limit of detection (LOD) for nucleic acid on nearly superhydrophobic surfaces was found to be 16.15 ng/µL, which was almost four-fold lower than on hydrophilic surfaces (60.08 ng/µL). Additionally, the LODs of standard glucose and clinical serum samples were two-fold lower on nearly superhydrophobic surfaces compared to hydrophilic surfaces. Our findings clearly highlight the promising potential of utilizing superhydrophobic surfaces to significantly enhance colorimetric sensitivity in paper-based diagnostic applications. This innovative approach holds promise for advancing point-of-care diagnostics and improving disease detection in resource-limited settings.

Implantable microfluidics: methods and applications

Implantable microfluidics involves integrating microfluidic functionalities into implantable devices, such as medical implants or bioelectronic devices, revolutionizing healthcare by enabling personalized and precise diagnostics, targeted drug delivery, and regeneration of targeted tissues or organs. The impact of implantable microfluidics depends heavily on advancements in both methods and applications. Despite significant progress in the past two decades, continuous advancements are still required in fluidic control and manipulation, device miniaturization and integration, biosafety considerations, as well as the development of various application scenarios to address a wide range of healthcare issues. In this review, we discuss advancements in implantable microfluidics, focusing on methods and applications. Regarding methods, we discuss progress made in fluid manipulation, device fabrication, and biosafety considerations in implantable microfluidics. In terms of applications, we review advancements in using implantable microfluidics for drug delivery, diagnostics, tissue engineering, and energy harvesting. The purpose of this review is to expand research ideas for the development of novel implantable microfluidic devices for various healthcare applications.

Development of Paper Microfluidics with 3D-Printed PDMS Barriers for Flow Control

Paper microfluidics has been extensively exploited as a powerful tool for environmental and medical detection applications. Both flow delay and compatibility with either polar or non-polar reagents are indispensable for the automation of detections requiring multiple reaction steps. This article reports the systematic studies of a 3D-printing protocol, characterization, and application of both the partially and fully penetrated polydimethylsiloxane (PDMS) barriers for flexible flow control in paper microfluidics. The physical parameters of PDMS barriers printed using a simple liquid dispenser were found related to the printing pressure, speed, diffusion time after printing, baking temperature, and PDMS viscosity. The capability of PDMS barriers to confine the flow of non-polar solvents was demonstrated using oil flow in both wax- and PDMS-surrounded channels. It was identified that the minimum width of channels to prevent leakage was 470 ± 54 μm, which was as narrow as that fabricated using stamps from lithography. Both the partially penetrated barriers (PPBs) and constriction channels were of the capability to delay flow in paper microfluidics. Additionally, an in silico investigation led to the further understanding that the reduction of channel cross-section resulting from PPBs was the primary reason for flow delay. Our results suggest that increasing the penetration depth of the barriers is more efficient in delaying flow than increasing the PPB length. Finally, devices with four inlet channels and 0-6 PPBs across each channel were successfully applied in flow delay for sequential fluid delivery. These results improve the understanding of the major factors, affecting the 3D PDMS barrier fabrication and the resulting flow control in paper microfluidics, providing practical implications for applications in various fields.

Paper-Based Molecular-Imprinting Technology and Its Application

Paper-based analytical devices (PADs) are highly effective tools due to their low cost, portability, low reagent accumulation, and ease of use. Molecularly imprinted polymers (MIP) are also extensively used as biomimetic receptors and specific adsorption materials for capturing target analytes in various complex matrices due to their excellent recognition ability and structural stability. The integration of MIP and PADs (MIP-PADs) realizes the rapid, convenient, and low-cost application of molecular-imprinting analysis technology. This review introduces the characteristics of MIP-PAD technology and discusses its application in the fields of on-site environmental analysis, food-safety monitoring, point-of-care detection, biomarker detection, and exposure assessment. The problems and future development of MIP-PAD technology in practical application are also prospected.

Embellishing 2-D MoS2 Nanosheets on Lotus Thread Devices for Enhanced Hydrophobicity and Antimicrobial Activity

Herein, we report cellulose-based threads from Indian sacred Lotus (Nelumbo nucifera) of the Nymphaceae family embellished with MoS₂ nanosheets for its enhanced hydrophobic and antimicrobial properties. MoS₂ nanosheets synthesized by a coprecipitation method using sodium molybdate dihydrate (Na₂MoO₄·2H₂O) and thioacetamide (CH₃CSNH₂) were used as a sourse for MoS₂ particle growth with cellulose threads extracted from lotus peduncles. The size, crystallinity, and morphology of pure and MoS₂-coated fibers were studied using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). the XRD pattern of pure lotus threads showed a semicrystalline nature, and the threads@MoS₂ composite showed more crystallinity than the pure threads. SEM depicts that pure lotus threads possess a smooth surface, and the MoS₂ nanosheets growth can be easily identified on the threads@MoS₂. Further, the presence of MoS₂ nanosheets on threads was confirmed with EDX elemental analysis. Antimicrobial studies with Escherichia coli and Candida albicans reveal that threads@MoS₂ have better resistance than its counterpart, i.e., pure threads. MoS₂ sheets play a predominant role in restricting the wicking capability of the pure threads due to their enhanced hydrophobic property. The water absorbency assay denotes the absorption rate of threads@MoS₂ to 80%, and threads@MoS₂ shows no penetration for the observed 60 min, thus confirming its wicking restriction. The contact angle for threads@MoS₂ is 128°, indicating its improved hydrophobicity.

Latex-Based Paper Devices with Super Solvent Resistance for On-the-Spot Detection of Metanil Yellow in Food Samples

The following paper presents a construct for a paper-based device which utilizes latex as the hydrophobic material for the fabrication of its hydrophobic barrier, which was deposited onto the cellulose surface either by free-hand or stenciled drawing. This method demands the least amount of expertise and time from its use, enabling a simple and rapid fabrication experience. Several properties of the hydrophobic material were characterized, such as the hydro head and penetration rate, with the aim of assessing its robustness and stability. The presented hydrophobic barriers fabricated using this approach have a barrier width of 4 mm, a coating thickness of 208 µm, and a hydrophilic resolution of 446.5 µm. This fabrication modality boasts an excellent solvent resistance with regard to the hydrophobic barrier. These devices were employed for on-the-spot detection of Metanil Yellow, a banned food adulterant often used in curcumin and pigeon peas, within successful limits of detection (LOD) of 0.5% (w/w) and 0.25% (w/w), respectively. These results indicate the great potential this fabricated hydrophobic device has in numerous paper-based applications and other closely related domains, such as diagnostics and sensing, signalling its capacity to become commonplace in both industrial and domestic settings.

Paper-based microfluidic devices for food adulterants: Cost-effective technological monitoring systems

Analytical sciences have witnessed emergent techniques for efficient clinical and industrial food adulterants detection. In this review, the contributions made by the paper-based devices are highlighted for efficient and rapid detection of food adulterants and additives, which is the need of the hour and how different categories of techniques have been developed in the past decade for upgrading the performance for point-of-care testing. A simple strategy with an arrangement for detecting specific adulterants followed by the addition of samples to obtain well-defined qualitative or quantitative signals for confirming the presence of target species. The paper-based microfluidics-based technology advances and prospects for food adulterant detection are discussed given the high-demand from the food sectors and serve as a valued technology for food researchers working in interdisciplinary technological frontiers.